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    <title>Document</title>
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  <style>
    /* 
    box-shadow:x延伸 y延伸 模糊半径 颜色
     */
    .div1 {
      height: 100px;
      width: 100px;
      background-color: pink;
      box-shadow: 5px 0px 5px red
    }

    span {
      background-color: yellow;
    }
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    <div class="div1"></div>
    <span>span</span>
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